Electric or hybrid machines are widely used as alternatives to their mechanical counterparts in industrial applications due to their higher efficiency and lower maintenance requirements. A high voltage power supply system is required for driving these electric machines. For the purpose of the present disclosure, high voltage refers to a voltage greater than 50 volts. The high voltage system usually includes one or more wire harnesses that enable the establishment of electrical power between the various systems of the electric machine. Non-limiting examples of wire harnesses include electrical conductors and connectors. These wire harnesses may be configured to pass various types of electrical signals, including DC voltage potentials and AC voltage signals.
The integrity of the high voltage harness is important to the reliability of the machine. For instance, if the connector components are not fully engaged or properly soldered, or crimped, or other types of connector faults occur, arcs may occur at the connector. Arcs usually contain high energy and generate a large amount of heat that may melt the connector and any conductive components. Therefore, it is desirable to test the harness system and detect connector degradation before arcs occur.
In order to achieve early detection, it is important that the testing system can adaptively account for operating characteristics of loads and sensor measurement errors. For example, each electric machine may include one or more electric loads. Depending on the operating characteristics of the electric loads, the currents flowing through these electric loads, as well as the voltages associated with them, may vary significantly. As a result, voltage levels at multiple points of a high voltage system may fluctuate significantly, depending on the electric loads connected to the system. For another example, sensor precision may also vary among different sensors and affect the voltage measurement.
One system for testing a wire harness in a high-voltage electrical circuit is described in Schoepf et al. U.S. Pat. No. 6,833,713 (“the '713 patent”). The '713 patent describes a wire harness testing system for detecting arc faults. The system includes two smart connectors connected in series with two terminals of a circuit portion being tested. Each smart connector includes electronic circuitry to measure both voltage and current. The system further includes two signal wires to transfer the values of the end voltage and end current from the end smart connector to the beginning smart wire. The testing system described in the '713 patent may compare the voltage difference between the two smart connectors with a preset value. In one instance, the wire harness testing system described in the '713 patent may further include a switching device that disconnects the power supply to the smart connectors in the event of arc faults.
Although the wire harness testing system described in the '713 patent may be effective for testing wire harness and detecting arc faults, it may be problematic. For example, the testing system described in the '713 patent is only capable of detecting an arc fault when it occurs, but does not provide early and preventative detection. For example, the system of the '713 patent does not use adaptive reference voltages and thus a voltage difference due to large resistance of electric loads being tested may be mistakenly detected as an arc fault.
Furthermore, the system described in the '713 patent may be too complex. For example, the system described in the '713 patent requires external smart connectors and additional wirings to perform the test. In addition, the solution provided by the '713 patent may not be convenient to use. For example, the wire harness test described in the '713 patent has to be formed manually by skilled electrical engineers since the system requires re-wiring and connection of external components.
The disclosed high voltage harness testing system is directed towards improvement in the existing technology.